1. Field of Invention
The present invention relates to means by which to provide incandescent lighting products operable to provide light at a particularly high degree of luminous efficacy.
2. Prior Art
Previous efforts at achieving significantly improved luminous efficacy in incandescent light bulbs--i.e., light bulbs adapted to screw into ordinary lamp sockets and to operate on 120 Volt RMS--have been directed toward the use of means operative to reflect infrared radiation back onto the incandescent filament while letting visible light pass through.
Examples of approaches of this nature are provided by numerous prior art references, such as the following U.S. Pat. No. 1,342,894 to Bugbee; No. 1,425,967 to Hoffman; No. 2,859,369 to Williams et al.; No. 4,039,878 to Eijkelenboom et al.; No. 4,160,929 to Thorington et al.; No. 4,283,653 to Brett; No. 4,366,407 to Walsh; and No. 4,375,605 to Fontana et al.
However, even though the basic principle has been known for decades, and even though the potentially attainable efficacy improvement is on the order of several hundred percent, household light bulbs based on this principle of selective reflection of infrared energy is not yet available on the market. The reason for this is apparently connected with difficulties in translating the basic principle into high-volume production of corresponding cost-effective household light bulbs.